Field of the Invention
The present invention generally relates to an apparatus and method for casing drilling. More particularly, the invention relates to apparatus and methods for sealing between two tubulars.
Description of the Related Art
In the oil and gas producing industry, the process of cementing casing into the wellbore of an oil or gas well generally comprises several steps. For example, a conductor pipe is positioned in the hole or wellbore and may be supported by the formation and/or cemented. Next, a section of a hole or wellbore is drilled with a drill bit which is slightly larger than the outside diameter of the casing which will be run into the well.
Thereafter, a string of casing is run into the wellbore to the required depth where the casing lands in and is supported by a well head in the conductor. Next, cement slurry is pumped into the casing to fill the annulus between the casing and the wellbore. The cement serves to secure the casing in position and prevent migration of fluids between formations through which the casing has passed. Once the cement hardens, a smaller drill bit is used to drill through the cement in the shoe joint and further into the formation.
Recently developed drilling with casing systems, such as Weatherford International's SeaLance™ system, a retrievable drilling motor is utilized to rotate the lower end of the casing string (or shoe track) independently of the remainder of the casing string. Due to the likelihood of misalignment during the drilling and cementing processes, a clearance gap exists between the lower end of the non-rotating casing string and the upper end of the rotating shoe track.
During drilling operations, it may be acceptable for a portion of the drilling fluid to leak through this gap, as fluid travels from the inside of the casing, through the gap, and into the annulus. Likewise, while pumping the cement slurry, it is acceptable for a portion of the cement slurry to leak through this gap, as it flows from the inside of the casing, through the gap, and into the annulus.
After pumping has stopped, it is important to prevent the cement slurry from u-tubing or flowing back from the annulus and into the inside of the casing. If this were to happen, a poor quality cement job could result. In addition, the retrievable drilling motor could become inadvertently cemented in place.
There is a need, therefore, for a reliable sealing mechanism that could effectively seal the gap between the shoe track and the casing string, when pumping stops.